The present disclosure relates generally to a strain gauge, particularly to a thin film strain gauge, and more particularly to an autoclavable thin film strain gauge.
Thin film strain gauges employing precision resistors in a Wheatstone bridge electrical circuit arrangement are known in the art.
Applicant has been using thin film vacuum deposition process to bond strain gauges directly to 15-5 stainless steel, Inconel, sapphire, and titanium for a number of years. A typical process begins by preparing the surface of the substrate with an abrasive slurry to remove all surface imperfections. The next step is the deposition of an oxide layer to insulate the circuit from the metal substrate. Following this, a thin film resistive alloy is sputtered over the oxide layer. This latter film is laser trimmed under power to produce the four resistors of the Wheatstone bridge. Solder pads are applied and wired to the circuit to provide a power egress and the whole thing is coated with an encapsulation to protect the thin film.
Over time, the thin film strain gauge has proven itself to be the preferred means for measuring strain in critical applications where small size, robust performance, long term stability and superior accuracy are required. An application of the thin film sensor technology is in the field of medical pump technology. When delivery of fluids to the body via infusion pumps, insulin pumps, enteral feed pumps, and wound irrigation systems is interrupted by a pinched tube or pump, undesired consequences may result. Often, ‘tube sensors’ are used to monitor pressure in these pump systems by measuring the force exerted onto a sensor pressed against the expanding walls of a polyurethane or PVC tubing or they place the sensor behind the pump to record pressures as the pump backs up against the sensor during operation. Thin film sensors have the repeatability and the ability to survive the rough handling and accuracy required to be successful in these pump applications.
However, such pump applications do not involve the surgical sterilization of a surgical device having a thin film strain gauge that is an integral part of the surgical device.
As such, and while existing thin film sensors may be suitable for their intended purpose, the art of thin film strain gauges would be advanced with a thin film strain gauge having the structural integrity to withstand exposure to multiple autoclave surgical-instrument sterilizing cycles and multiple surgical-instrument cleaning detergent cycles without statistically significant loss in accuracy.
This background information is provided to reveal information believed by the applicant to be of possible relevance to the present invention. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present invention.